Wüstite is a transition metal oxide (that is, iron (II) oxide) that carries several advantages, including being cheap, non-toxic, and has a band gap in the optimal range for absorbing solar energy. One disadvantage of wüstite is that it suffers from thermodynamic instability in the bulk phase, but can alternatively be used in the nanophase (wüstite has been observed as a nano-film and as nanometer-sized islands. References: Galloway, H C., Benitez, J. J., and Salmeron, M. Surf. Science 1993, 298, 127; Wang, W., Zhang, H., Wang, W., Zhao, A., Wang, B., and Huo, J. G. Chem. Phys. Lett. 2010, 500, 76), or as an alloy with other stable oxides. The low conductivity of wüstite is another major disadvantage that limits its capability to transport charge carriers after photon absorption, toward producing electricity or fuel. Wüstite also has conduction and valence band edges with the same orbital character that may lead to unfavorably high electron-hole recombination rates. Another limitation of iron (II) oxide is that the calculated valence band edge is not positioned well for oxidizing water. Furthermore, unlike wüstite, other oxides, including magnesium (II) oxide, manganese (II) oxide, nickel (II) oxide, and zinc (II) oxide, have band gaps that are too large for efficiently absorbing light. It would be desirable to provide improved wüstite compositions that address these and other shortcomings.